/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:		arm_rms_q15.c
*
* Description:	Root Mean Square of the elements of a Q15 vector.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated.
* ---------------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @addtogroup RMS
 * @{
 */

/**
 * @brief Root Mean Square of the elements of a Q15 vector.
 * @param[in]       *pSrc points to the input vector
 * @param[in]       blockSize length of the input vector
 * @param[out]      *pResult rms value returned here
 * @return none.
 *
 * @details
 * <b>Scaling and Overflow Behavior:</b>
 *
 * \par
 * The function is implemented using a 64-bit internal accumulator.
 * The input is represented in 1.15 format.
 * Intermediate multiplication yields a 2.30 format, and this
 * result is added without saturation to a 64-bit accumulator in 34.30 format.
 * With 33 guard bits in the accumulator, there is no risk of overflow, and the
 * full precision of the intermediate multiplication is preserved.
 * Finally, the 34.30 result is truncated to 34.15 format by discarding the lower
 * 15 bits, and then saturated to yield a result in 1.15 format.
 *
 */

void arm_rms_q15(
    q15_t* pSrc,
    uint32_t blockSize,
    q15_t* pResult)
{
	q63_t sum = 0;                                 /* accumulator */

#ifndef ARM_MATH_CM0

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	q31_t in;                                      /* temporary variable to store the input value */
	q15_t in1;                                     /* temporary variable to store the input value */
	uint32_t blkCnt;                               /* loop counter */

	/* loop Unrolling */
	blkCnt = blockSize >> 2u;

	/* First part of the processing with loop unrolling.  Compute 4 outputs at a time.
	 ** a second loop below computes the remaining 1 to 3 samples. */
	while(blkCnt > 0u) {
		/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		/* Compute sum of the squares and then store the results in a temporary variable, sum */
		in = *__SIMD32(pSrc)++;
		sum = __SMLALD(in, in, sum);
		in = *__SIMD32(pSrc)++;
		sum = __SMLALD(in, in, sum);

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* If the blockSize is not a multiple of 4, compute any remaining output samples here.
	 ** No loop unrolling is used. */
	blkCnt = blockSize % 0x4u;

	while(blkCnt > 0u) {
		/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		/* Compute sum of the squares and then store the results in a temporary variable, sum */
		in1 = *pSrc++;
		sum = __SMLALD(in1, in1, sum);

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* Truncating and saturating the accumulator to 1.15 format */
	sum = __SSAT((q31_t)(sum >> 15), 16);

	in1 = (q15_t)(sum / blockSize);

	/* Store the result in the destination */
	arm_sqrt_q15(in1, pResult);

#else

	/* Run the below code for Cortex-M0 */

	q15_t in;                                      /* temporary variable to store the input value */
	uint32_t blkCnt;                               /* loop counter */

	/* Loop over blockSize number of values */
	blkCnt = blockSize;

	while(blkCnt > 0u) {
		/* C = (A[0] * A[0] + A[1] * A[1] + ... + A[blockSize-1] * A[blockSize-1]) */
		/* Compute sum of the squares and then store the results in a temporary variable, sum */
		in = *pSrc++;
		sum += ((q31_t) in * in);

		/* Decrement the loop counter */
		blkCnt--;
	}

	/* Truncating and saturating the accumulator to 1.15 format */
	sum = __SSAT((q31_t)(sum >> 15), 16);

	in = (q15_t)(sum / blockSize);

	/* Store the result in the destination */
	arm_sqrt_q15(in, pResult);

#endif /* #ifndef ARM_MATH_CM0 */

}

/**
 * @} end of RMS group
 */
